As methods for improving the workability of ferritic stainless steel sheets, for example, a method has been disclosed in Japanese Unexamined Patent Application Publication No. 3-264652 in which Ti or Nb is added besides reduction of C and N. In addition, in Japanese Unexamined Patent Application Publication No. 5-320772, as methods for manufacturing a more inexpensive Ti-containing ferritic stainless steel sheet, a manufacturing method has been disclosed in which besides hot rolling control performed by high temperature coiling, precipitation of FeTiP, which causes hardening and decrease in ductility, is suppressed by controlling the contents of P, S, C and N so that annealing of hot-rolled steel sheets can be omitted.
As is the above method, in Japanese Unexamined Patent Application Publication No. 10-204588, a method for manufacturing stainless steel sheets having superior workability has been disclosed. In this method, the upper limits of P, C, S, and N contents forming phosphides, carbides, nitrides, and sulfides with Ti are controlled for suppressing the precipitation of phosphides, carbides, and sulfides in coiling of a hot-rolled steel sheet so as to facilitate recrystallization in the coiling mentioned above, and as a result, although annealing of a hot-rolled steel sheet is omitted, a stainless steel sheet having superior workability can be manufactured. In the above three conventional techniques, P and C precipitates, and P and C in a solid solution form are regarded as elements harmful to the workability, and it has been believed that it is important to reduce the contents of P and C as small as possible by refining.
The reduction of P and C contained in steel by refining described above is effective for improvement in steel properties; however, the reduction described above may cause some problems in some cases. For example, the following may be mentioned.    (1) When recycling of dust and slag by-produced in a steel-manufacturing process and reuse of scrap are taken into consideration, in order to reduce the contents of P and C in steel, which inevitably come from the starting materials mentioned above, to a predetermined level, refining for a long period of time is required in a steel-manufacturing process, and as a result, the productivity is decreased.    (2) By the reduction of the elements described above, it becomes difficult to control the growth of steel grains, and concomitant with larger and coarser grain diameters of a hot-rolled steel sheet, the anisotropy is increased, resulting in apparent generation of ridging (surface irregularities) and the like.
An object of the present invention is to provide stainless steel and a manufacturing method thereof, the stainless steel having improved workability and properties such as a yield strength. In the stainless steel described above, P present therein is allowed to remain to a certain extent by refining so that a load required for refining is decreased, and in addition, P in the form of larger and coarser Ti base precipitates is positively precipitated so as to make P harmless. In addition, an object of the present invention is to enable existing machines to be efficiently used without enhancing the capacities thereof and is to achieve recycling of steel materials and energy saving in manufacturing.